Resin film for a terminal and energy storage device using the same

ABSTRACT

A resin film for a terminal which includes at least three layers, which define a first outer surface and a second outer surface of the resin film, the first outer surface being opposed to the second outer surface; a first adhesive layer which is one of the three layers and is arranged to form the first outer surface of the resin film; a second adhesive layer which is one of the three layers and is arranged to form the second outer surface of the resin film; and an insulating layer which is arranged between the first adhesive layer and the second adhesive layer. The first adhesive layer contains first polypropylene and second polypropylene. The first polypropylene has a long-chain branched structure. The second polypropylene has no long-chain branched structure and has a melting point of 80° C. to 155° C.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation application filed under 35 U.S.C. §111(a) claiming the benefit under 35 U.S.C. §§ 120 and 365(c) ofInternational Patent Application No. PCT/JP2021/001853, filed on Jan.20, 2021, which in turn claims the benefit of JP 2020-079387, filed Apr.28, 2020 the disclosures of all which are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to a resin film for a terminal,and an energy storage device using the same.

BACKGROUND ART

In recent years, there have been increasing demands for miniaturizationof portable devices or effectively using electrical energy generatedfrom natural resources. Therefore, to meet the demands, research anddevelopment has been conducted to produce lithium-ion secondarybatteries (a type of energy storage device) from which higher voltagesare available and in which electrical energy can be stored at anincreased density.

In the past, metallic cans have often been used as a package for suchlithium ion cells. However, to meet the demands for thinner and morediversified products to which the lithium ion batteries are applied,pouched laminates in which a metal layer (such as an aluminum foil) anda resin film are laminated, which can be produced at low cost, havebecome common as a package.

A laminate type lithium ion secondary battery which has a battery bodydisposed and sealed in the package is equipped with a current outputterminal usually referred to as a tab. The tab includes a metal terminal(sometimes also referred to as a “tab lead”) and a resin film for aterminal (sometimes also referred to as a “tab sealant”) (see forexample, PTLs 1 to 3). The metal terminal is connected to the negativeelectrode or positive electrode of the battery body and extended to thepackage (packaging material). The resin film for a terminal covers apart of the outer peripheral surface of the metal terminal. The resinfilm for a terminal is usually fused to the metal terminal.

[Citation List] [Patent Literatures] PTL 1: JP 2008-4316 A; PTL 2: JP2010-218766 A; PTL 3: JP 2009-259739 A.

SUMMARY OF THE INVENTION Technical Problem

In recent years, battery packs have been increasingly exposed to hightemperatures due to an increase in the temperature of chemicalconversion process in manufacturing batteries and thermal runaway causedby rapid charging. Exposing a battery pack to a high temperatureenvironment leads to a problem of decreasing the adhesion between thepackaging material and the tab sealant.

The purpose of the present disclosure is to provide a resin film for aterminal and an energy storage device using the same. The resin film fora terminal has excellent adhesion between a packaging material and ametal terminal under a room temperature environment and can sufficientlymaintain the adhesion to the packaging material even when exposed to ahigh temperature environment.

Solution to Problem

To achieve the above-mentioned objects, the present disclosure providesa resin film for a terminal which includes at least three layers. Theresin film covers a part of an outer peripheral surface of a metalterminal. The metal terminal is electrically connected to an energystorage device body of an energy storage device. The resin film includesat least three layers which define a first outer surface and a secondouter surface of the resin film, the first outer surface being opposedto the second outer surface; a first adhesive layer which is one of thethree layers and is arranged to form the first outer surface of theresin film; a second adhesive layer which is one of the three layers andis arranged to form the second outer surface of the resin film; and aninsulating layer which is arranged between the first adhesive layer andthe second adhesive layer. The first adhesive layer contains firstpolypropylene and second polypropylene. The first polypropylene has along-chain branched structure. The second polypropylene has nolong-chain branched structure and has a melting point of 80° C. to 155°C.

As a result of intensive study, the inventor of the present inventionhas found that the reason why the adhesion between the packagingmaterial and the tab sealant decreases when exposed to a hightemperature environment is that an electrolyte undergoes foaming in thehigh temperature environment and thus a gap is formed between thepackaging material and the tab sealant. In addition, it was found thatthe foaming of the electrolyte occurred frequently, especially in thetab sealant on the packaging material side of the energy storage device.As a result of further study, the inventor of the present invention hasfound that it is possible to suppress foaming starting from a tabsealant by arranging a layer in contact with the packaging material. Thepackaging material contains polypropylene having a long-chain branchedstructure, and polypropylene having no long-chain branched structure andhaving a melting point of 80° C. to 155° C.

In the resin film for a terminal, polypropylene having the long-chainbranched structure may have a content of 1 mass % to 50 mass % relativeto a total amount of the first adhesive layer. If the content of thepolypropylene having a long-chain branched structure is 1 mass % to 50mass % relative to the total amount of the first adhesive layer, theadhesion between the resin film for a terminal and the packagingmaterial is better, and curling of the resin film for a terminal can befurther suppressed.

In the resin film for a terminal, the polypropylene having a long-chainbranched structure may be polypropylene synthesized using a metallocenecatalyst. Since the polypropylene having a long-chain branched structureis polypropylene synthesized using a metallocene catalyst, the adhesionbetween the resin film for a terminal and the packaging material isimproved, and the adhesion between the resin film for a terminal and thepackage can be better maintained even when exposed to a high temperatureenvironment.

In the resin film for a terminal, the ratio of the thickness of thesecond adhesive layer to the thickness of the first adhesive layer(second adhesive layer/first adhesive layer) may be 0.2 to 4.5. Sincethe ratio of the thickness of the second adhesive layer to the thicknessof the first adhesive layer is 0.2 to 4.5, curling of the resin film fora terminal can be further suppressed.

In the resin film for a terminal, the absolute difference between themelting point of the first adhesive layer and the melting point of thesecond adhesive layer may be 0° C. to 15° C. Since the absolutedifference between the melting point of the first adhesive layer and themelting point of the second adhesive layer is 0° C. to 15° C., curlingof the resin film for a terminal can be further suppressed.

In the resin film for a terminal, the first adhesive layer and/or theinsulating layer may contain a filler. If the first adhesive layerand/or the insulating layer contain a filler, the adhesion between theresin film for a terminal and the packaging material can be maintainedeven when exposed to a high temperature environment.

In the resin film for a terminal, the second adhesive layer may containa resin having a polar group. If the second adhesive layer contains aresin having a polar group, the adhesion between the resin film for aterminal and the metal terminal is improved.

The present disclosure also provides an energy storage device including:an energy storage device body; a metal terminal which is electricallyconnected to the energy storage device body; a packaging material whichgrips the metal terminal therein and has the energy storage device bodydisposed therein; and a resin film for a terminal which is disposedbetween the metal terminal and the packaging material and which covers apart of the outer peripheral surface of the metal terminal, wherein thefirst adhesive layer is in contact with the packaging material and thesecond adhesive layer is in contact with the metal terminal. Such anenergy storage device provides excellent adhesion between the packagingmaterial and the metal terminal under a room temperature environment,and can sufficiently maintain the adhesion between the resin film for aterminal and the packaging material even when exposed to a hightemperature environment.

Advantageous Effects of the Invention

According to the present disclosure, a resin film for a terminal and anenergy storage device using the same provide excellent adhesion betweena packaging material and a metal terminal under a room temperatureenvironment, and can sufficiently maintain adhesion to the packagingmaterial even when exposed to a high temperature environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a schematic configuration ofan energy storage device according an embodiment of the presentdisclosure.

FIG. 2 is a cross-sectional view illustrating an example of across-section of the packaging material shown in FIG. 1 .

FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 1 ,illustrating the resin film for a terminal and the metal terminal shownin FIG. 1 .

FIG. 4 is a schematic diagram illustrating a method of producingspecimens for measuring a heat seal strength in the Examples.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below withreference to the drawings. In the following description of the drawingsto be referred, components or functions identical with or similar toeach other are given the same or similar reference signs, unless thereis a reason not to. It should be noted that the drawings are onlyschematically illustrated, and thus the relationship between thicknessand two-dimensional size of the components, and the thickness ratiobetween the layers, are not to scale. Therefore, specific thicknessesand dimensions should be understood in view of the followingdescription. As a matter of course, dimensional relationships or ratiosmay be different between the drawings.

Further, the embodiments described below are merely examples ofconfigurations for embodying the technical idea of the presentinvention. The technical idea of the present invention does not limitthe materials, shapes, structures, arrangements, and the like of thecomponents to those described below. The technical idea of the presentinvention can be modified variously within the technical scope definedby the claims. The present invention is not limited to the followingembodiments within the scope not departing from the spirit of thepresent invention. For the sake of clarity, the drawings may beillustrated in an exaggerated manner as appropriate.

In any group of successive numerical value ranges described in thepresent specification, the upper limit value or lower limit value of onenumerical value range may be replaced with the upper limit value orlower limit value of another numerical value range. In the numericalvalue ranges described in the present specification, the upper limitvalues or lower limit values of the numerical value ranges may bereplaced with values shown in examples. The configuration according to acertain embodiment may be applied to other embodiments.

The embodiments of the present invention are a group of embodimentsbased on a single unique invention. The aspects of the present inventionare those of the group of embodiments based on a single invention.Configurations of the present invention can have aspects of the presentdisclosure. Features of the present invention can be combined to formthe configurations. Therefore, the features of the present invention,the configurations of the present invention, the aspects of the presentdisclosure, and the embodiments of the present invention can becombined, and the combinations can have a synergistic function andexhibit a synergistic effect.

FIG. 1 is a perspective view illustrating a schematic configuration ofan energy storage device according to an embodiment of the presentdisclosure. FIG. 1 shows a lithium ion secondary battery as an exampleof an energy storage device 10. The following description is provided byway of this example. The lithium ion secondary battery, whoseconfiguration is shown in FIG. 1 , is often called a battery pack or abattery cell.

The energy storage device 10 shown in FIG. 1 is a lithium ion secondarybattery, and includes an energy storage device body 11, a packagingmaterial 13, a pair of metal terminals 14 (tab leads), and a resin filmfor a terminal 16 (tab sealant).

The energy storage device body 11 is a battery that performs charging ordischarging. The packaging material 13 grips the metal terminal 14therein and has the energy storage device body 11 disposed therein. Thepackaging material 13 covers the surface of the energy storage devicebody 11 and is in contact with a part of the resin film for a terminal16.

FIG. 2 is a cross-sectional view illustrating an example of a crosssection of the packaging material shown in FIG. 1 . In FIG. 2 , the samecomponents as those shown in FIG. 1 are denoted by the same referencesigns.

Referring now to FIG. 2 , an example of a configuration of the packagingmaterial 13 will be described. The packaging material 13 is structuredin seven layers which include an inner layer 21, an inner layer-sideadhesive layer 22, an anti-corrosion treatment layer 23-1, a metal layerserving as a barrier layer 24, an anti-corrosion treatment layer 23-2,an outer layer-side adhesive layer 25, and an outer layer 26. The layersare laminated in this order from an inner side of the packaging material13 in contact with the energy storage device body 11.

For example, the inner layer 21 is a sealant layer that imparts sealingproperties to the packaging material 13 by heat sealing, and is a layerwhich is arranged inside and heat-sealed when the energy storage device10 is assembled. Base materials that can be used for the inner layer(sealant layer) 21 include, for example, polyolefin resins, oracid-modified polyolefin resins obtained by graft-modifying polyolefinresins with maleic anhydrides. The polyolefin resins that can be usedinclude: low-density, medium-density and high-density polyethylenes;ethylene-α-olefin copolymers; homo-, block- or random-polypropylenes;and propylene-α-olefin copolymers. Among these, the polyolefin resinpreferably contains polypropylene. These polyolefin resins may be usedsingly or in combination of two or more.

Furthermore, depending on the required functions, the inner layer 21 maybe formed using a single-layer film or a multilayer film in which aplurality of layers are laminated. For example, in order to impartmoisture resistance, a multilayer film interposed with a resin such asethylene-cyclic olefin copolymer or polymethylpentene may be used. Inaddition, the inner layer 21 may contain, for example, various additives(such as flame retarders, slip agents, anti-blocking agents,antioxidants, light stabilizers, tackifiers, and the like).

For example, the thickness of the inner layer 21 is preferably set in arange of 10 μm to 150 μm, and more preferably 30 μm to 80 μm. When thethickness of the inner layer 21 is 10 μm or more, the heat seal adhesionbetween the packaging materials 13 and the adhesion to the resin filmfor a terminal 16 are sufficiently high. Furthermore, when the thicknessof the inner layer 21 is 150 μm or less, an increase in the cost of thepackaging material 13 can be suppressed.

As the inner layer-side adhesive layer 22, a known adhesive can beappropriately selected and used, such as a generally used adhesive fordry lamination or an acid-modified thermally adhesive resin.

As shown in FIG. 2 , it is preferable that the anti-corrosion treatmentlayers 23-1 and 23-2 are formed on both surfaces of the barrier layer 24from the viewpoint of performance. However, taking account of cost, theanti-corrosion treatment layer 23-1 alone may be arranged on the innerlayer-side adhesive layer 22 side surface of the barrier layer 24.

The barrier layer 24 is, for example, a metal layer having electricalconductivity. The barrier layer 24 may be made of, for example,aluminum, stainless steel, or the like, but aluminum is preferable fromthe perspective of cost or weight (density).

As the outer-layer side adhesive layer 25, for example, a generalpolyurethane adhesive containing polyester polyol, polyether polyol, oracrylic polyol as a main resin can be used.

Layers that can be used for the outer layer 26 include, for example,single-layer films or multi-layer films such as nylon or polyethyleneterephthalate (PET). Similar to the inner layer 21, the outer layer 26may contain various additives (e.g. flame retarders, slip agents,anti-blocking agents, antioxidants, light stabilizers, tackifiers, andthe like), for example. Furthermore, the outer layer 26 may include, asa measure against fluid leakage, a protective layer formed, for example,by laminating a resin which is insoluble in an electrolyte, or coating aresin component which is insoluble in an electrolyte.

FIG. 3 is a cross-sectional view taken along the line A-A of FIG. 1illustrating a resin film for a terminal and a metal terminal. In FIG. 3, components identical with those of the structure shown in FIG. 1 aregiven the same reference signs.

As shown in FIGS. 1 and 3 , a pair (two in FIG. 1 ) of metal terminals14 each include a metal terminal body 14-1 and an anti-corrosion layer14-2. Of the pair of metal terminal bodies 14-1, one metal terminal body14-1 is electrically connected to a positive electrode of the energystorage device body 11, and the other metal terminal body 14-1 iselectrically connected to a negative electrode of the energy storagedevice body 11. The pair of metal terminal bodies 14-1 extend in adirection away from the energy storage device body 11, while beingpartially exposed from the packaging material 13. The pair of terminalbodies 14-1 may be in a plate-like shape, for example.

The metal terminal bodies 14-1 may be made of a metal. The metal used asthe material for the metal terminal bodies 14-1 is preferably determinedin consideration of the structure of the energy storage device body 11and the materials of the respective components of the energy storagedevice body 11.

For example, when the energy storage device 10 is a lithium ionsecondary battery, aluminum is used as a positive electrode currentcollector, while copper is used as a negative electrode currentcollector. For this case, aluminum is preferably used as the materialfor the metal terminal body 14-1 which is connected to the positiveelectrode of the energy storage device body 11. Furthermore, takingaccount of corrosion resistance to an electrolyte, an aluminum material,such as 1N30 having purity of 97% or more is preferably used, forexample, as a material for the metal terminal body 14-1 connected to thepositive electrode of the energy storage device body 11. In addition,when the metal terminal body 14-1 is bent, an annealed metal materialwhich is heat-treated by sufficient annealing is preferably used for thepurpose of adding flexibility. As a material used for the metal terminalbody 14-1 connected to the negative terminal of the energy storagedevice body 11, it is preferable to use copper whose surface is providedwith a nickel-plated layer, or to use nickel.

The thickness of the metal terminal bodies 14-1 can be set according tothe size or capacity of the lithium ion secondary battery. When thelithium ion secondary battery is of a small size, the thickness of themetal terminal bodies 14-1 is preferably 50 μm or more, for example.When the lithium ion secondary battery is of a large size so as to beapplicable such as to electrical storage and vehicle installation, thethickness of the metal terminal bodies 14-1 can be appropriately set towithin the range of 100 μm to 500 μm, for example.

The anti-corrosion layer 14-2 is arranged covering at least part of thesurface of the metal terminal body 14-1. Lithium ion secondary batteriesinclude an electrolyte that contains corrosive components, such asLiPF₆. The anti-corrosion layer 14-2 minimizes corrosion of the metalterminal body 14-1 caused by the corrosive components, such as LiPF₆,contained in the electrolyte.

As shown in FIG. 3 , the resin film for a terminal 16 covers a part ofthe outer peripheral surface of the metal terminal 14. In the presentembodiment, the resin film for a terminal 16 includes at least threelayers. The three layers are a second adhesive layer (hereinafter alsoreferred to as the innermost layer) 31, a first adhesive layer(hereinafter also referred to as the outermost layer) 32, and aninsulating layer (also referred to as the intermediate layer) 33, whichare laminated. The second adhesive layer 31 is in contact with the outerperipheral side surface of the metal terminal 14, the first adhesivelayer 32 is in contact with the packaging material 13, and theinsulating layer 33 is disposed between the innermost layer 31 and theoutermost layer 32. The first adhesive layer 32 is arranged to form oneouter surface of the resin film for a terminal 16, and the secondadhesive layer 31 is arranged on a surface opposite to the firstadhesive layer of the resin film for a terminal 16. The resin film for aterminal 16 may include layers in addition to the innermost layer, theoutermost layer, and the intermediate layer.

The innermost layer 31, which covers the outer peripheral surface of themetal terminal 14, seals the metal terminal 14 in the circumferentialdirection of the metal terminal 14, while achieving adhesion between theresin film for a terminal 16 and the metal terminal 14. The outermostlayer 32 also has a function of sealing the interior of the packagingmaterial 13 by being fused with the packaging material 13.

[Innermost Layer]

In the present embodiment, the innermost layer 31 is a layer fused tothe metal terminal. The innermost layer 31 preferably contains a resinhaving a polar group (hereinafter also referred to as “polar resin”)from the viewpoint of better adhesion to the metal terminal. Examples ofthe polar group include a hydroxyl group, a glycidyl group, an amidegroup, an imino group, an oxazoline group, an acid anhydride group, acarboxyl group, and an ester group. From the viewpoint of reactivity, anacid anhydride group (particularly a group derived from maleicanhydride) is preferable as the polar group. Examples of the polar resininclude the modified polyolefin having the polar group,polyhydroxypolyolefin oligomers, and ethylene/acrylic acid/glycidylmethacrylate copolymers. The polar resin is preferably a polyolefinmodified with an acid anhydride such as maleic anhydride from theviewpoint of reactivity. Examples of the polyolefin includepolypropylene, polyethylene, and polybutene.

As the polypropylene, homopolypropylene, random polypropylene, blockpolypropylene, or low isotactic polypropylene can be used. Among these,random polypropylene or low isotactic polypropylene is preferable fromthe viewpoint of adhesion to the metal terminal, openability under hightemperature environment, and impact resistance. The modifiedpolypropylene is polypropylene having the polar group as describedabove, and is preferably an acid-modified polypropylene, and morepreferably an acid-modified random polypropylene.

Specific examples of polar resins include “Poval” manufactured byKuraray Co., Ltd. and “Melthene H” manufactured by Tosoh Corporation aspolar resins having a hydroxy group, “MODIPER” manufactured by NOFCORPORATION “LOTADER” and “BONDINE” manufactured by Arkema Inc. as polarresins having a glycidyl group, “APOLHYA” manufactured by Arkema Inc. aspolar resins having an amide group, “ADMER IP” manufactured by MitsuiChemicals, Inc. as polar resins having an imino group, and “EPOCROS”manufactured by Nippon Shokubai Co., Ltd. as polar resins having anoxazoline group. The modified resin may be used singly or in combinationof two or more.

The melting point of the polar resin is preferably 80° C. to 160° C.,more preferably 100° C. to 150° C., and even more preferably 110° C. to145° C., from the viewpoint of embeddability and heat resistance.

The melting point of resin, as referred to in the present specification,is the temperature when the heat of dissolution reaches a peak top whichis referred to as a main peak. The temperature is measured using adifferential scanning calorimeter (DSC).

The content of the polar resin in the innermost layer 31 is preferably40 mass % or more relative to the total amount of the innermost layer31, from the viewpoint of better adhesion with the metal terminal. Theupper limit of the content of the polar resin is not particularlylimited, but may be 99 mass % or less, and may be 95 mass % or less.

The innermost layer 31 may contain a resin other than a polar resin.Examples of the resin other than the polar resin include polyolefinssuch as polypropylene, polyethylene, and polybutene.

In the innermost layer 31, the content of resin other than the polarresin may be 1 mass % to 20 mass % relative to the total amount of theinnermost layer 31. When the content of resin other than the polar resinis 1 mass % or more, the adhesion between the innermost layer 31 and themetal terminal tends to further increase. When the content of resinother than the polar resin is 20 mass % or less, decrease in thecohesive force can be suppressed and the sufficient adhesion between theinnermost layer 31 and the metal terminal can be maintained.

The innermost layer 31 may include additives other than the componentdescribed above. Examples of the additive include antioxidants, slipagents, flame retardants, light stabilizers, dehydrating agents,coloring pigments, tackifiers, and the like. These can be used singly orin combination of two or more. Examples of the coloring pigment includecarbon black, quinacridone pigments, polyazo pigments, and isoindolinonepigments.

The innermost layer 31 preferably has a thickness in the range of 10 μmto 100 m, and more preferably in the range of 15 μm to 50 μm. Theinnermost layer 31 having a thickness of 10 μm or more provides betteradhesion to the metal terminal 14. The innermost layer 31 having athickness of 100 μm or less suppresses an increase in the cost of theresin film for a terminal 16.

[Outermost Layer]

In the present embodiment, the outermost layer 32 is, for example, alayer to be fused with a packaging material. The outermost layer 32contains polypropylene having a long-chain branched structure andpolypropylene having no long-chain branched structure and having amelting point of 80° C. to 155° C. When the outermost layer containspolypropylene having a long-chain branched structure, and polypropylenehaving no long-chain branched structure and having a melting point of80° C. to 155° C., adhesion to the packaging material under a roomtemperature environment is excellent and the adhesion to the packagingmaterial can be sufficiently maintained even when exposed to a hightemperature environment.

Polypropylene having a long-chain branched structure (hereinafter alsoreferred to as “long-chain branched PP”) refers to polypropylene havinga branched structure with a molecular chain having several tens or morecarbon atoms in the main chain and an average molecular weight ofseveral hundred or more. The polypropylene having a long-chain branchedstructure may be a homopolymer of propylene or a copolymer. Whenpropylene having a long-chain branched structure is a copolymer, thecomonomer may be at least one kind of olefin selected from the groupconsisting of ethylene and α-olefins having 4 to 10 carbon atoms, andthe content of the comonomer in the long-chain branched PP is preferably3 mass % or less. The long chain branched PP is preferably a propylenehomopolymer because it has higher heat resistance and rigidity.

The long-chain branched PP can be produced by a method of electroncrosslinking or by synthesis using a metallocene catalyst. From theviewpoint of suppressing gel generation and obtaining sufficientstrength, it is preferable that the long-chain branched PP issynthesized using a metallocene catalyst. The fact that long-chainbranched PP has been synthesized using the metallocene catalyst can beconfirmed by analyzing the catalyst residue using analytical methodssuch as infrared spectroscopy (IR), NMR spectroscopy, mass spectrometry(MS), X-ray analysis, and Raman spectroscopy.

The melting point of the long-chain branched PP is preferably 100° C. to170° C. and more preferably 130° C. to 160° C., from the viewpoint ofembeddability and heat resistance.

In the outermost layer 32, the content of the long-chain branched PP ispreferably 1 mass % to 50 mass %, more preferably 3 mass % to 30 mass %,and still more preferably 5 mass % to 20 mass % relative to the totalamount of the outermost layer 32. When the content of the long-chainbranched PP is 1 mass % or more, foaming in the outermost layer can befurther suppressed. When the content of the long-chain branched PP is 50mass % or less, embeddability is improved, and sufficient adhesion withthe packaging material can be maintained, and also curling of the resinfilm for a terminal can be further suppressed.

Polypropylene having no long-chain branched structure and having amelting point of 80° C. to 155° C. refers to polypropylene having amelting point of 80° C. to 155° C., and does not correspond topolypropylene having a long-chain branched structure as described above.The polypropylene having no long-chain branched structure and having amelting point of 80° C. to 155° C. may be a homopolypropylene having amelting point of 80° C. to 155° C., a random polypropylene, a blockpolypropylene, a low isotactic polypropylene, or the like. Thepolypropylene having no long-chain branched structure and having amelting point of 800 to 155° C. may be modified.

The melting point of the polypropylene having no long-chain branchedstructure and having a melting point of 80° C. to 155° C. is morepreferably 100° C. to 150° C., and even more preferably 105° C. to 145°C. from the viewpoint of adhesion to the packaging material and heatresistance.

The outermost layer 32 preferably contains a filler from the viewpointof further suppressing foaming in the outermost layer. The filler may bean inorganic filler such as aluminum oxide, silicon oxide, magnesiumoxide, zirconium oxide, calcium carbonate, zirconium silicate, zincoxide, barium sulfate, copper oxide, cobalt oxide, titanium oxide, tinoxide, iron oxide, antimony oxide, boron nitride, aluminum nitride,silicon nitride, or the like. These can be used singly or in combinationof two or more. The filler preferably has an average particle size inthe range of 0.1 μm to 25 μm. The content of the filler is preferably0.05 mass % to 10 mass %, and more preferably 0.1 mass % to 5 mass %relative to the total amount of the outermost layer 32. The fillercontent of 0.05 mass % or more further suppresses the decrease in theadhesion due to foaming. The filler content of 10 mass % or lessmaintains sufficient adhesion to the packaging material.

Resins and additives other than those described above may be added tothe outermost layer 32. Examples of the additive include antioxidants,slip agents, flame retarders, light stabilizers, dehydrating agents,coloring pigments, tackifiers, and the like. These can be used singly orin combination of two or more. Examples of the coloring pigment includecarbon black, quinacridone pigments, polyazo pigments, and isoindolinonepigments.

The outermost layer 32 preferably has a thickness in the range of 10 to100 μm, and more preferably in the range of 15 to 50 μm. The outermostlayer 32 having a thickness of m or more provides better adhesion to thepackaging material 13. The outermost layer 32 having a thickness of 100μm or less suppresses an increase in the cost of the resin film for aterminal 16.

The melting points of the innermost layer 31 and the outermost layer 32are the temperature when the heat of dissolution reaches a peak topwhich is referred to as a main peak, and can be set to the meltingpoints of each layer. The temperature is measured using a differentialscanning calorimeter (DSC). The absolute difference (difference inabsolute value) between the melting point of the innermost layer 31 andthe melting point of the outermost layer 32 is preferably 0° C. to 15°C., more preferably 0° C. to 10° C., and even more preferably 0° C. to5° C., from the viewpoint of further suppressing curling of the resinfilm for a terminal.

[Intermediate Layer]

The intermediate layer 33 is arranged between the innermost layer 31 andthe outermost layer 32. One surface of the intermediate layer 33 may becovered with the innermost layer 31, and the other surface may becovered with the outermost layer 32.

The intermediate layer 33 includes an insulating layer. The insulatinglayer is a layer that prevents the sealant (the sealant layer of thepackaging material and the innermost layer and the outermost layer ofthe resin film for a terminal) from flowing out during heat sealing andcausing the exposed metal layer of the packaging material to come intocontact with the metal terminals, thereby degrading the insulation.Therefore, the insulating layer is preferably formed using a resinhaving a high melting point or glass transition temperature, which doesnot flow out during heat sealing.

As the resin constituting the insulating layer, for example,polyethylene terephthalate, polyethylene naphthalate, polyphenylenesulfide, polymethylpentene, polyacetal, cyclic polyolefin, polyamide,polycarbonate, polyphenylene ether, polypropylene and the like can beused. Among these, from the viewpoint of film forming properties,interlayer adhesion, and impact resistance, polypropylene may preferablybe used, and block polypropylene is particularly preferable. Theseresins preferably have a melting point or a glass transition temperature(Tg) higher than that of the resin used in the innermost layer 31 andthe outermost layer 32. These resins may be used singly or incombination of two or more.

The insulating layer preferably contains a filler from the viewpoint offurther suppressing foaming in the outermost layer. The above-mentionedinorganic filler which can be used in the outermost layer can besimilarly used as the filler. These can be used singly or in combinationof two or more. The filler preferably has an average particle size inthe range of 0.1 μm to 25 μm. The content of the filler is preferably0.1 mass % to 30 mass %, and more preferably 1 mass % to 15 mass %relative to the total amount of the insulating layer (intermediate layer33). The filler content of 0.1 mass % or more further suppresses thedecrease in the adhesion due to foaming. The filler content of 30 mass %or less maintains sufficient embeddability.

The insulating layer may be colored by adding a coloring pigment to theinsulating layer. The visibility of the resin film for a terminal 16 canbe improved by coloring the insulating layer. Thus, accuracy is improvedin inspecting the resin film for a terminal 16 (for example, ininspecting whether the resin film for a terminal 16 is attached to themetal terminal 14, or in inspecting the position where the resin filmfor a terminal 16 is attached relative to the metal terminal 14).Examples of the coloring pigment include copper oxide, cobalt oxide,zinc oxide, titanium oxide, carbon black, barium sulfate, quinacridonepigments, polyazo pigments, and isoindolinone pigments.

The intermediate layer 33 may further include a layer having aconfiguration other than the above-described insulating layer.Specifically, the intermediate layer 33 may be a single-layer structureconsisting of an insulating layer, or may be a multilayer structurehaving a plurality of resin layers in addition to the insulating layervia an adhesive. The intermediate layer 33 may include, for example, alayer containing a resin having a crosslinked structure (crosslinkedlayer), or a layer containing at least one kind selected from the groupconsisting of fillers and fibers (reinforcing layer).

Examples of the resin having a crosslinked structure in the crosslinkedlayer include crosslinked acrylic resin, epoxy resin, phenol resin, urearesin, melamine resin, and polyurethane resin. These can be used singlyor in combination of two or more.

The filler used for the reinforcing layer may be the same as that forthe insulating layer. The content of the filler is preferably 0.5 mass %to 20 mass % relative to the total amount of the reinforcing layer.

The fibers of the reinforcing layer may be a cellulose resin or a resinhaving a melting point of 200° C. or higher used for the heat-resistantlayer. These can be used singly or in combination of two or more. Thewidth of the fibers is preferably from 10 nm to 10 μm, and the contentof the fibers may be preferably from 0.5 mass % to 70 mass % relative tothe total amount of the reinforcing layer. The fibers may also form anonwoven fabric.

The reinforcing layer can be a layer in which the filler and/or thefiber mentioned above is dispersed in the polyolefin resin, the resinhaving a melting point of 200° C. or higher, or the resin having acrosslinked structure.

The thickness of the intermediate layer 33 (the entire thickness in thecase of a multilayer structure) is, for example, appropriately set inthe range of 10 μm to 200 μm, and is preferably 20 μm to 100 μm. Interms of the thickness of the intermediate layer 33, it is importantthat there is a balance between the thickness of the metal terminal 14and the thickness of the innermost layer 31. Therefore, when theinnermost layer 31 and the metal terminal 14 are thick, the thickness ofthe intermediate layer 33 may have a large thickness accordingly.

The total thickness of the innermost layer 31, the outermost layer 32,and the intermediate layer 33 (thickness of the resin film for aterminal 16) is, from the viewpoint of the heat-sealing properties, andembeddability and insulating properties of the metal terminal,preferably from 10 μm to 500 μm, more preferably from 15 μm to 300 μm,and even more preferably from 30 μm to 200 μm.

The ratio of thicknesses of the innermost layer 31, the intermediatelayer 33, and the outermost layer 32 (the innermost layer 31: theintermediate layer 33: the outermost layer 32) may be for example 2:1:2,1:2:1, and 1:1:1, and the thicknesses of the innermost layer 31 and theoutermost layer 32 may be the same when the intermediate layer 33 servesas the insulating layer. The ratio of the thicknesses of the innermostlayer 31, the intermediate layer 33, and the outermost layer 32 (theinnermost layer 31: the intermediate layer 33: the outermost layer 32)may be for example 3:1:1, 2:2:1, or 5:3:2, and the thickness of theinnermost layer 31 in contact with the metal terminal may be larger thanthe thickness of the outermost layer 32, from the viewpoint ofembeddability of the metal terminal. Alternatively, the ratio of thethicknesses of the innermost layer 31, the intermediate layer 33, andthe outermost layer 32 may be for example 1:1:3, 1:2:2, or 2:3:5, andthe thickness of the outermost layer 32 in contact with the packagingmaterial may be thicker than the thickness of the innermost layer 31,from the viewpoint of adhesion to the packaging material.

When the thicknesses of the innermost layer 31 and the outermost layer32 are the same, the ratio of the thickness of the innermost layer 31 orthe outermost layer 32 to the thickness of the intermediate layer 33(innermost layer 31 or outermost layer 32: intermediate layer 33) may be1:3 to 3:1, or 1:2 to 2:1. When the thickness of the innermost layer 31is different from the thickness of the outermost layer 32, the ratio ofthe thickness of the innermost layer 31 to the thickness of theintermediate layer 33 (the innermost layer 31: the intermediate layer33) may be 4:1 to 1:1, or may be 3:1 to 1:1. The ratio of the thicknessof the outermost layer 32 to the thickness of the intermediate layer 33(the outermost layer 32: the intermediate layer 33) may be 1:3 to 3:1,or may be 1:2 to 2:1. The ratio of the thickness of the innermost layer31 to the thickness of the outermost layer 32 (the innermost layer 31:the outermost layer 32) may be 1:5 to 9:2, more preferably 3:10 to 7:2,and even more preferably 2:5 to 5:2, from the viewpoint of furthersuppressing curling of the resin film for a terminal. That is, the ratioof the thickness of the innermost layer to the thickness of theoutermost layer (innermost layer/outermost layer) is preferably 0.2 to4.5, more preferably 0.3 to 3.5, and even more preferably 0.4 to 2.5,from the viewpoint of further suppressing curling of the resin film fora terminal.

While a preferred embodiment of the present disclosure has beendescribed above, the present disclosure is not limited to this specificembodiment, and various alterations and modifications can be made withinthe scope of the present disclosure as defined in the appended claims.

For example, in FIG. 3 , a resin film for a terminal 16 having athree-layer structure has been described as an example. However, asecond intermediate layer composed of an insulating resin and the likemay be disposed between the intermediate layer 33 and the innermostlayer 31, and between the intermediate layer 33 and the outermost layer32.

By arranging a second intermediate layer between the intermediate layer33 and the innermost layer 31, and between the intermediate layer 33 andthe outermost layer 32 to form a multilayer structure having four ormore layers, it is possible to improve the insulation properties betweenthe intermediate layer 33 and the barrier layer 24 (metal layer)constituting the packaging material 13, and the insulation propertiesbetween the intermediate layer 33 and the metal terminal 14. The secondintermediate layer may also be the crosslinked layer or the reinforcinglayer described above.

Furthermore, the innermost layer 31 and the outermost layer 32 may havethe same configuration as each other, or may have differentconfigurations to each other. Specifically, in the resin film for aterminal of the present disclosure, at least one of the layers on thesurface of the resin film for a terminal may satisfy the requirements ofthe outermost layer, and the other layer need not satisfy therequirements of the outermost layer. Therefore, one of the innermostlayer 31 and the outermost layer 32 may be a layer containingpolypropylene having a long-chain branched structure and polypropylenehaving no long-chain branched structure and having a melting point of80° C. to 155° C., and the other may be a layer containing one or bothof polypropylene having a long-chain branched structure andpolypropylene having no long-chain branched structure and having amelting point of 80° C. to 155° C.

Next, a method of producing the resin film for a terminal 16 of thepresent embodiment will be briefly described. The method of producingthe resin film for a terminal 16 is not particularly limited. The resinfilm for a terminal 16 can be fabricated using a film-extrusionfabrication device having a die, such as a round die used in inflationmolding or a T-die used in die pressing. However, from the viewpoint offilm formation stability, multilayer inflation molding is preferablyused.

The following description addresses a method for producing the resinfilm for a terminal 16 by way of an example of using inflation molding(i.e. using an inflation molding apparatus).

Firstly, base materials for the innermost layer 31, the outermost layer32, and the intermediate layer 33 are prepared. Then, the base materialsof the innermost layer 31, the outermost layer 32, and the intermediatelayer 33 are supplied to an inflation molding apparatus. Then, the threebase materials are extruded from an extrusion part of the inflationmolding apparatus to form a three-layer structure (structure in whichthe innermost layer 31, the outermost layer 32, and the intermediatelayer 33 are laminated) and air is supplied from inside the laminate.

Then, while conveying the cylindrically inflated resin film for aterminal 16, the resin film for a terminal 16 is formed into a flatshape by a guide section, and then a pair of pinch rolls folds the resinfilm for a terminal 16 into a sheet shape. Both sides of the woven tubeare cut open and a pair (two strips) of film is rolled onto a take-upcore to produce a rolled resin film for a terminal 16.

For example, the extrusion temperature at which the resin film for aterminal 16 is produced is preferably in the range of 130° C. to 300°C., and more preferably in the range of 130° C. to 250° C. When theextrusion temperature is 130° C. or higher, the resin constituting eachlayer is sufficiently melted, resulting in a lower melt viscosity, whichmakes extrusion from a screw more stable. On another front, when theextrusion temperature is 300° C. or lower, oxidation and deteriorationof the resin constituting each layer is suppressed. As a result, it ispossible to prevent a decrease in quality of the resin film for aterminal 16.

The revolution speed, blow ratio, pulling speed, and the like of eachscrew can be appropriately determined taking account of the filmthickness that has been set. Furthermore, the thickness ratio of thelayers of the resin film for a terminal 16 can be easily controlled bychanging the revolution speed of each of the screws.

The resin film for a terminal 16 of the present embodiment may beproduced through dry lamination using an adhesive, or through sandwichlamination in which formed insulating layers (insulating films) arelaminated to each other.

Referring to FIG. 3 , a thermal adhesion process will be described inwhich the resin film for a terminal 16 and the packaging material 13 ofthe present embodiment are thermally adhered to each other. For example,in the thermal adhesion process, melting of the outermost layer 32 byheating is conducted concurrently with achieving intimate contactbetween the outermost layer 32 and the packaging material 13 bypressing, thereby thermally adhering the resin film for a terminal 16and the packaging material 13 to each other.

Furthermore, in the thermal adhesion process described above, in orderto obtain sufficient adhesion and sealing properties between the resinfilm for a terminal 16 and the packaging material 13, heating isconducted to a temperature of at least the melting point of the resinwhich constitutes the outermost layer 32.

Specifically, for example, a temperature in the range of 140° C. to 170°C. can be used as a heating temperature for the resin film for aterminal 16. The processing time (the total time of the heating time andthe pressing time) may be determined in consideration of peelingstrength and productivity. The processing time can be appropriately setin the range of 1 to 60 seconds, for example.

When the production takt (productivity) of the resin film for a terminal16 is prioritized, thermal adhesion may be conducted with a shorterpressing time at a temperature exceeding 170° C. In this case, theheating temperature can be in the range of 170° C. to 230° C., forexample, while the pressing time can be in the range of 3 seconds to 20seconds, for example.

Referring to FIG. 3 , a thermal adhesion process will be described inwhich the resin film for a terminal 16 and the metal terminal 14 of thepresent embodiment are thermally adhered to each other. For example, inthe thermal adhesion process, melting of the innermost layer 31 byheating is conducted concurrently with achieving intimate contactbetween the innermost layer 31 and the metal terminal 14 by pressing,thereby thermally adhering the resin film for a terminal 16 and themetal terminal 14 to each other.

Furthermore, in the thermal adhesion process described above, in orderto obtain sufficient adhesion between the resin film for a terminal 16and the metal terminal 14, and sealing properties, heating is conductedto a temperature of at least the melting point of the resin whichconstitutes the innermost layer 31.

Specifically, for example, a temperature in the range of 140° C. to 170°C. can be used as a heating temperature for the resin film for aterminal 16. The processing time (the total time of the heating time andthe pressing time) may be determined in consideration of peelingstrength and productivity. The processing time can be appropriately setin the range of 1 to 60 seconds, for example.

When the production takt (productivity) of the resin film for a terminal16 is prioritized, thermal adhesion may be conducted with a shorterpressing time at a temperature exceeding 170° C. In this case, theheating temperature can be in the range of 170° C. to 230° C., forexample, while the pressing time can be in the range of 3 seconds to 20seconds, for example.

EXAMPLES

The present disclosure will be more specifically described below basedon Examples and Comparative Examples. However, the present disclosure isnot limited to the following Examples.

[Materials Used]

Materials used in examples and comparative example are shown in Table 1below.

TABLE 1 Melting Component Detail point (° C.) Polypropylene having A1Synthesized using 157 a long-chain branched a metallocene catalyststructure (long-chain A2 Synthesized by 160 branched PP) electroncrosslinking Polypropylene having B1 Acid-modified random PP 140 nolong-chain branched B2 Acid-modified random PP 105 structure (PP) B3Acid-modified random PP 155 B4 Acid-modified low 106 isotactic PP B5Acid-modified homo PP 165 B6 Random PP 140 Base PP C1 Block PP 165 Polarresin D1 Polyhydroxypolyolefin 65 oligomer Filler E1 Silicon oxide — E2Titanium oxide —

[Preparation of Resin Film for a Terminal]

Examples 1 to 15 and Comparative Examples 1 to 4

The base materials for each layer were prepared by dry blending eachingredient in the amounts (unit: mass %, abbreviated as “%” in thetable) shown in Table 2. Measurement of the heat of fusion of each filmby DSC resulted in detecting peaks corresponding to the melting point ofeach resin component. The absolute difference between the melting pointof the outermost layer and that of the innermost layer is shown in Table2.

Then, the base material of the first adhesive layer (outermost layer),the base material of the insulating layer (intermediate layer), and thebase material of the second adhesive layer (innermost layer) were setinside an inflation type film extrusion production device (Co-GI type)manufactured by Sumitomo Heavy Industries Modern Ltd., and the threebase materials were extruded using the film extrusion production deviceto produce a resin film for a terminal having a three-layer structurecomposed of outermost layer/intermediate layer/innermost layer (however,Comparative Example 4 is a resin film for a terminal having a two-layerstructure composed of intermediate layer/innermost layer). The meltingtemperature of each base material was 210° C. The thickness of eachlayer in the resin film for a terminal of each Example was as shown in“thickness [μm] of outer/middle/inner” in Table 2. The“outer/medium/inner” in Table 2 means the outermost layer (outer)/mediumlayer (middle)/inner layer (inner).

[Measurement of Initial (Room Temperature) Heat Seal Strength of Lead]

A specimen obtained by cutting the resin film for a terminal into a sizeof 50 mm (TD)×100 mm (MD) was folded in two so as to sandwich achemically treated aluminum foil cut to a size of 50 mm×50 mm, and theside on the opposite side to the folded section was heat sealed at 165°C./0.6 MPa/10 seconds with a width of 10 mm. Then, a specimen for theheat seal strength measurement was prepared by cutting the heat-sealedportion to a width of 15 mm at a center portion of a length of theheat-sealed portion (see FIG. 4 ). In the present evaluation, thelaminate 100 in FIG. 4 is made of the resin film for a terminal/aluminumfoil/resin film for a terminal. A T-peel test to peel the aluminum foil(lead) and the resin film of the heat-sealed portion of the specimenaway from each other was performed for the heat-sealed portion of thespecimen using a tensile tester (manufactured by Shimadzu Corporation)under room temperature (25° C.) environmental conditions and a tensilespeed of 50 mm/min. From the obtained results, the initial heat sealstrength of the lead was evaluated based on the following evaluationcriteria. “A”, “B”, or “C” in the evaluation columns represents“acceptable” and “D” represents “unacceptable”. The results are shown inTable 2.

A: Heat seal strength of 25 N/15 mm or more

B: Heat seal strength of 20 N/15 mm or more and less than 25 N/15 mm

C: Heat seal strength of 15 N/15 mm or more and less than 20 N/15 mm

D: Heat seal strength of less than 15 N/15 mm

[Measurement of Initial (Room Temperature) Heat Seal Strength ofPackaging Material]

A specimen obtained by cutting the resin film for a terminal into a sizeof 50 mm (TD)×100 mm (MD) was folded in two so as to sandwich achemically treated aluminum foil cut to a size of 50 mm×50 mm, and theside on the opposite side to the folded section was heat sealed at 165°C./0.6 MPa/10 seconds with a width of 10 mm. Then, the sealant layer ofthe packaging material, which has a laminated structure composed of anylon film (thickness: 25 μm)/adhesive agent/aluminum foil (thickness:40 μm)/polypropylene sealant layer (thickness: 80 μm) was folded intotwo so as to make contact with the resin film for a terminal, and theside on the opposite side to the folded portion (the same location asthe location in which the resin film for a terminal and the aluminumfoil was heat sealed) was heat sealed at 190° C./0.5 MPa/5 seconds witha width of 10 mm. Then, a specimen for the heat seal strengthmeasurement was prepared by cutting the heat-sealed portion to a widthof 15 mm at a center portion of a length of the heat-sealed portion (seeFIG. 4 ). In this evaluation, the laminate 100 in FIG. 4 is composed ofa packaging material, a resin film for a terminal, an aluminum foil, aresin film for a terminal, and a packaging material. A T-peel test topeel the packaging material and the resin film for a terminal of theheat-sealed portion of the specimen away from each other was performedfor the heat-sealed portion of the specimen using a tensile tester(manufactured by Shimadzu Corporation) under room temperature (25° C.)environmental conditions and a tensile speed of 50 mm/min. From theobtained results, the initial heat seal strength of the packagingmaterial was evaluated based on the following evaluation criteria. “A”,“B”, or “C” in the evaluation columns represents “acceptable” and “D”represents “unacceptable”. The results are shown in Table 2.

A: Heat seal strength of 100 N/15 mm or more

B: Heat seal strength of 90 N/15 mm or more and less than 100 N/15 mm.

C: Heat seal strength of 80 N/15 mm or more and less than 90 N/15 mm

D: Heat seal strength of less than 80 N/15 mm

[Heat Seal Strength of Packaging Material Against Electrolyte]

A specimen obtained by cutting the resin film for a terminal into a sizeof 50 mm (TD)×100 mm (MD) was folded in two so as to sandwich achemically treated aluminum foil cut to a size of 50 mm×50 mm, and theside on the opposite side to the folded section was heat sealed at 165°C./0.6 MPa/10 seconds with a width of 10 mm. Then, the sealant layer ofthe packaging material, which has a laminated structure composed of anylon film (thickness: 25 μm)/adhesive agent/aluminum foil (thickness:40 μm)/polypropylene sealant layer (thickness: 80 μm) was folded intotwo so as to make contact with the resin film for a terminal, and theside on the opposite side to the folded portion (the same location asthe location in which the resin film for a terminal and the aluminumfoil was heat sealed) was heat sealed at 190° C./0.5 MPa/5 seconds witha width of 10 mm. Then, the remaining two sides excluding the foldedportion were heat sealed in the same manner as the side on the oppositeside to the folded portion. A pouch is made by heat sealing one of theremaining two sides, injecting 1 mL of an electrolyte into the otherside, and then heat sealing the other side. The electrolyte was made byadding 1M of LiPF₆ (lithium hexafluorophosphate) to a mixed solution ofethylene carbonate/diethyl carbonate/dimethyl carbonate=1/1/1 (massratio). After the prepared pouch was stored at 90° C. for 1 week, thecenter portion of a length of the heat-sealed portion at the side on theopposite side to the folded portion was cut out with a width of 15 mm(see FIG. 4 ) to prepare a specimen for measuring the heat sealstrength. In this evaluation, the laminate 100 in FIG. 4 is composed ofa packaging material, a resin film for a terminal, an aluminum foil, aresin film for a terminal, and a packaging material. A T-peel test topeel the packaging material and the resin film for a terminal of theheat-sealed portion of the specimen away from each other was performedfor the heat-sealed portion of the specimen using a tensile tester(manufactured by Shimadzu Corporation) under room temperature (25° C.)environmental conditions and a tensile speed of 50 mm/min. From theobtained results, the heat seal strength of the packaging materialagainst electrolyte was evaluated based on the following evaluationcriteria. “A”, “B”, or “C” in the evaluation columns represents“acceptable” and “D” represents “unacceptable”. The results of theevaluation and the seal strength are shown in Table 2.

A: Heat seal strength of 70 N/15 mm or more

B: Heat seal strength of 60 N/15 mm or more and less than 70 N/15 mm.

C: Heat seal strength of 50 N/15 mm or more and less than 60 N/15 mm

D: Heat seal strength of less than 50 N/15 mm

[Curlability Assessment]

A specimen of resin film for a terminal cut into a size of 50 mm(TD)×100 mm (MD) was placed on a smooth surface, and the heights fromthe smooth surface were measured at four apexes. The curlability wasevaluated using the average of the four heights based on the followingevaluation criteria. “A”, “B”, or “C” in the evaluation columnsrepresents “acceptable” and “D” represents “unacceptable”. The resultsare shown in Table 2.

A: Curl height being less than 15 mm

B: Curl height being 15 mm or more and less than 20 mm

C: Curl height being 20 mm or more and less than 25 mm

D: Curl height being 25 mm or more

TABLE 2 Evaluation result Heat seal Room strength temper- of packagingResin film for a terminal Room ature material Thick- Adhesive layerInsulating layer Adhesive temper- heat seal against ness (outermostlayer) (intermediate layer) layer Thick- Melting ature strengthelectrolyte [μm] Long- Long- (innermost ness point heat seal of Sealouter/ chain chain layer) ratio differ- strength pack- strength middle/branched branched Base Polar inner/ ence of aging Eval- N/15 Curla-inner PP PP Filler PP PP Filler PP resin outer [° C.] lead materialuation mm bility Ex 1 25/50/ A1 B1 E1 — C1 E2 B1 — 1.0 0 A A A 84 A 2515% 84% 1% 95% 5% 100% Ex 2 25/50/ A1 B1 E1 — C1 E2 B1 — 1.0 0 A B A 77B 25 40% 59% 1% 95% 5% 100% Ex 3 25/50/ A2 B1 E1 — C1 E2 B1 — 1.0 0 A BB 65 A 25 15% 84% 1% 95% 5% 100% Ex 4 25/50/ A1 B1 — — C1 — B1 — 1.0 9.0A A A 71 A 25 15% 85% 100% 100% Ex 5 25/50/ A1 B1 E1 — C1 — B1 — 1.0 0 AA A 79 A 25 15% 84% 1% 100% 100% Ex 6 25/50/ A1 B1 E1 — C1 E2 B1 — 1.0 0A B A 73 A 25 15% 78% 1% 75% 25% 100% Ex 7 20/40/ A1 B1 E1 — C1 E2 B1 —2.0 0 A A A 82 A 40 15% 84% 1% 95% 5% 100% Ex 8 20/30/ A1 B1 E1 — C1 E2B1 — 2.5 0 A A A 81 A 50 15% 84% 1% 95% 5% 100% Ex 9 15/40/ A1 B1 E1 —C1 E2 B1 — 3.0 0 A A A 80 B 45 15% 84% 1% 95% 5% 100% Ex 10 10/40/ A1 B1E1 — C1 E2 B1 — 5.0 0 A A A 77 C 50 15% 84% 1% 95% 5% 100% Ex 11 25/50/A1 B2 E1 — C1 E2 B1 — 1.0 35.0 A A A 86 C 25 15% 84% 1% 95% 5% 100% Ex12 25/50/ A1 B3 E1 — C1 E2 B1 — 1.0 10.0 A A A 80 B 25 15% 84% 1% 95% 5%100% Ex 13 25/50/ A1 B4 E1 — C1 E2 B1 — 1.0 34.0 A A A 85 C 25 15% 84%1% 95% 5% 100% Ex 14 25/50/ A1 B1 E1 — C1 E2 B6 D1 1.0 0.0 B A A 84 A 2515% 84% 1% 95% 5% 85% 15% Ex 15 25/50/ A1 B1 E1 — C1 E2 B6 — 1.0 0.0 C AA 86 A 25 15% 84% 1% 95% 5% 100% Comp 25/50/ — B1 E1 — C1 E2 B1 — 1.00.0 A A D 38 A Ex 1 25 99% 1% 95% 5% 100% Comp 25/50/ — B1 E1 A1 C1 E2B1 — 1.0 0.0 A A D 40 A Ex 2 25 99% 1% 15% 80% 5% 100% Comp 25/50/ A1 B5E1 — C1 E2 B1 — 1.0 024 A D D 21 C Ex 3 25 15% 84% 1% 95% 5% 100% Comp0/50/ — — A1 C1 E2 B1 — — — A D D 25 D Ex 4 50 15% 80% 5% 100% Ex =Example, Comp Ex = Comparative Example

REFERENCE SIGNS LIST

10 . . . Energy storage device; 11 . . . Energy storage device body; 13. . . Packaging material; 14 . . . Metal terminal; 14-1 . . . Metalterminal body; 14-2 . . . Anticorrosion layer; 16 . . . Terminal resinfilm; 21 . . . Inner layer; 22 . . . Inner layer-side adhesive layer;23-1, 23-2 . . . Anti-corrosion treatment layer; 24 . . . Barrier layer;25 . . . Outer layer-side adhesive layer; 26 . . . Outer layer; 31 . . .Innermost layer; 32 . . . Outermost layer; 33 . . . Intermediate layer.

What is claimed is:
 1. A resin film for a terminal, covering a part ofan outer peripheral surface of a metal terminal, the metal terminalbeing electrically connected to an energy storage device body of anenergy storage device, the resin film comprising: at least three layersthat define a first outer surface and a second outer surface of theresin film, the first outer surface being opposed to the second outersurface; a first adhesive layer that is one of the three layers andarranged to form the first outer surface of the resin film; a secondadhesive layer that is one of the three layers and arranged to form thesecond outer surface of the resin film; and an insulating layer that isarranged between the first adhesive layer and the second adhesive layer,wherein the first adhesive layer contains first polypropylene and secondpolypropylene, the first polypropylene having a long-chain branchedstructure, the second polypropylene having no long-chain branchedstructure and having a melting point of 80° C. to 155° C.
 2. The resinfilm for a terminal of claim 1, wherein the first polypropylene having along-chain branched structure has a content of 1 mass % to 50 mass %relative to a total amount of the first adhesive layer.
 3. The resinfilm for a terminal of claim 1, wherein the first polypropylene having along-chain branched structure is synthesized using a metallocenecatalyst.
 4. The resin film for a terminal of claim 1, wherein a ratioof a thickness of the second adhesive layer to a thickness of the firstadhesive layer is 0.2 to 4.5.
 5. The resin film for a terminal of claim1, wherein an absolute difference between a melting point of the firstadhesive layer and a melting point of the second adhesive layer is 0° C.to 15° C.
 6. The resin film for a terminal of claim 1, wherein the firstadhesive layer and/or the insulating layer contains a filler.
 7. Theresin film for a terminal of claim 1, wherein the second adhesive layercontains a resin having a polar group.
 8. An energy storage device,comprising: an energy storage device body; a metal terminal which iselectrically connected to the energy storage device body; a packagingmaterial which grips the metal terminal therein and has the energystorage device body disposed therein; and the resin film for a terminalof claim 1 that covers a part of an outer peripheral surface of themetal terminal, the resin film being disposed between the metal terminaland the packaging material, wherein the first adhesive layer is incontact with the packaging material, the second adhesive layercontacting the metal terminal.